Study of Nozzle Fouling: Deposit Build-Up and Removal

The global demand for decreased emission from engines and increased efficiency drives manufactures to develop more advanced fuel injection systems. Today's compression-ignited engines use common rail systems with high injection pressures and fuel injector nozzles with small orifice diameters. These systems are highly sensitive to small changes in orifice diameters since these could lead to deteriorations in spray characteristics, thus reducing engine performance and increasing emissions. Phenomena that could create problems include nozzle fouling caused by metal carboxylates or biofuels. The problems increase with extended use of biofuels. This paper reports on an experimental study of nozzle hole fouling performed on a single-cylinder engine. The aim was to identify if the solubility of the fuel has an effect on deposit build-up and, thus, the reduction in fuelling with associated torque loss, and if there is a probability of regenerating the contaminated injectors. Additionally, the influence of the nozzle geometry was tested by using injectors of various designs. In the experiments, high-load engine operation was used to create the effect of fouling in the presence of zinc-neodecanoate. Solubility properties of the fuel were tested by using high- and low-aromatic-content diesel fuels. To gain insight into the morphology and chemical characteristics of the deposits, the nozzles were opened and examined with scanning electron microscopy/energy dispersive x-ray (SEM/EDX). The results showed higher power loss in low-aromatic-content fuels. The experiments also showed regained engine power within an hour using uncontaminated fuel in a fouled nozzle. A three steps process is proposed as the mechanism for deposit build-up and removal in injector nozzles. It is suggested that fouling of the injector is equilibrium between the different steps of the mechanisms.